The present invention relates to laminated nuts utilizing laminations of hex shaped, coned-disc springs, having a central opening tapped to match threads on an associated bolt and more specifically to a laminated nut having an anti-spin off structure and a method for making such nut and is a continuation in part of U.S. patent application of Richard L. Reynolds Ser. No. 388,658, filed Aug. 2, 1989 now U.S. Pat. No. 4,940,377 for Laminated Nut Having Cage With Nested Fingers and Method of Manufacture and the disclosure thereof is incorporated herein by reference.
Laminated nuts have stacked, aligned multiple discs retained by a steel outer cage which can be hex shaped and having six fingers. Examples of such laminated nut structures are shown and described in U.S. Pat. No. 4,383,787, issued to Reynolds on May 17, 1983. Another type with only two fingers which are in a nested construction is shown in my noted copending patent application Ser. No. 388,658.
The above noted laminated nuts are free running on the bolt until seated in clamping workpieces together. A locking force between the nut and bolt results from the application of additional torque and rotation after initial seating. The additional torque compresses and partially flattens the conical spring discs whereby a mechanical interference occurs between the thread flanks of the nut and bolt; it is believed that this is at least partially due to a change in hole size of the nut as the conical discs flatten. The resultant thread interference and retained spring load between thread flanks resists unloading that might otherwise occur as a result of tensile or vibrational loads. Thus, the independently loaded conical spring threaded segments when flattened create a thread interference that tends to lock the nut against rotation or loosening when subject to such loads.
It is conventional to utilize discs which are hardened whereby permanent deformation is resisted. In some instances one of the discs is constructed of a non-hardened material. Upon final installation in clamping the workpieces together the soft disc is permanently deformed causing a thread inference; thus when the nut is reverse torqued the interference remains creating a prevailing torque characteristic. Until such deformation, however, the nut is free running and can be readily spun onto the associated bolt.
At the same time, however, unless the nut is torqued to clamp the workpieces to a selected magnitude, the locking action is not implemented and/or the deformation causing the prevailing torque characteristic does not occur. Here the free running nut could, if not properly loaded, back off from the bolt. Thus in some applications it is desirable that the laminated nut provide a prevailing torque even for the initial application onto the bolt; in these situations the nut would not be free running. Thus in the event the operator fails to fully torque the nut onto the bolt to create the lock and/or the prevailing torque deformation, the nut will still have a prevailing torque feature resisting removal and hence resisting loosening and/or backing off from the bolt through vibration.
In the present invention a unique laminated nut construction is provided having a soft disc interspersed with a plurality of hard discs with the soft disc designed to provide the prevailing torque feature after deformation from final torquing. In addition, however, the soft disc is initially predeformed at a plurality of locations to provide a preselected interference with the mating thread of the bolt; this initial interference will provide resistance to torquing on but will also provide resistance to backing off in the event the nut has not been properly torqued on. The result will be a prevailing torque characteristic which will resist backing off in the event the nut has not been adequately tightened on the bolt to properly clamp the workpieces. The pre-deformed or initial magnitude of prevailing torque is selected to be relatively small compared to the magnitude of the final prevailing torque such that initial installation torque loads in running the nut onto the bolt can be minimized.
The cage can be formed with a cup portion and a plurality of fingers that engage the discs to hold them in alignment. In the present invention openings are provided in the fingers in line with the soft disc such that the soft disc can be accessed by a plurality of punches; in this way the soft disc can be struck at a plurality of positions to deform the threaded opening to provide interference with the threaded bolt resulting in the desired initial magnitude of prevailing torque. The nut is heat treated after assembly and after thread formation; it appears that, as a side benefit, the presence of the openings in the cage fingers permits a more uniform exposure to the heating atmosphere resulting in a better, more uniform heat treat of the discs to be hardened. It is believed that this effect is most beneficial with the hex shaped cage of the type shown in the noted '787 patent.
It appears desirable to deform the soft disc or washer through openings in fingers even with the nested, two finger cage construction of the referenced ,658 patent application. When the soft disc is deformed at sides which have no fingers there is a tendency for the discs to separate axially disturbing the continuity of the threads in the threaded bore. This can result in high friction and galling of the associated bolt. Such axial separation is avoided when the deformation is made through openings in the fingers; in this regard it appears that the fingers act locally to axially clamp the discs together and hence inhibit axial separation.
Therefore, it is an object of the present invention to provide an improved laminated nut structure having a plurality of hardened discs and a soft disc with the soft disc having its thread form distorted prior to installation of the nut on the bolt to provide an initial prevailing torque characteristic with the associated bolt.
It is another object to provide an improved laminated nut having a cage with a plurality of retaining fingers with the fingers having openings in the areas of a soft disc to permit access for upsetting the soft disc whereby the noted thread interference for the initial prevailing torque characteristic can be provided.
It is another object to provide an improved laminated nut structure having a plurality of hardened discs and a soft disc with the threads of the soft disc deformed to provide an initial magnitude of prevailing torque as it is applied to an associated bolt and to provide a final magnitude of prevailing torque as it is again distorted by the application of the final magnitude of torque in clamping workpieces together.
It an object of the present invention to provide a unique laminated nut structure.
It is still another object to provide a unique method of making a laminated nut having a novel prevailing torque characteristic.
Other objects, features, and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, in which: